In submerged arc welding, an advancing welding wire moves through a granular flux so an electric arc between the wire and workpiece melts the advancing wire and deposits a weld metal onto the workpiece. The flux is at least partially melted during the welding process and forms a slag over the top of the molten metal deposited on the workpiece. The slag is designed to protect the molten metal from the ingress of atmospheric impurities. When forming a tough weld metal, it has been common practice to use small amounts of titanium and boron as an additive to the flux. In such fluxes, the slag system itself is not based upon titanium dioxide (e.g., rutile). The flux disclosed in the present invention has a high Basicity Index (BI) so that fine grain structure is obtained by use of small amounts of titanium and boron. Toughness of a weld metal is commonly determined by a Charpy test. High toughness weld metal normally requires use of a high BI (i.e., BI exceeding about 2). It has been found that a highly basic flux that includes small amounts of titanium and boron produces a fine grain size and a high toughness weld metal, thus resulting in a significant improvement of prior art welding fluxes. These patents are incorporated by reference herein as background information on fluxes to which the present invention is directed. Although it is known in the art to use small amounts of titanium and boron in a granular flux to create a Ti Bor weld metal, this weld metal often must be reheated after solidification to refine the grain size of the weld metal.
Many prior highly basic fluxes do not use a titanium dioxide slag system. As such, when titanium and boron were added to such flux systems, a relatively large amount of titanium dioxide or titanium powder was added to such flux systems. The large addition of a titanium source to the flux system resulted in at least about 20 ppm of titanium to be deposited in the weld metal. This higher level of titanium in the weld metal resulted in poor slag removal from the weld metal. A flux system that included a rutile based slag system drastically increased the amount of titanium in the weld metal, resulting in even more difficult slag removal from the weld bead. Even though the large amounts of titanium in the weld metal made it more difficult to remove slag from the weld bead, high levels of titanium were believed to be required to from the necessary toughness of the weld metal. In prior flux systems that included boron, the boron content was maintained at quite low levels since only a very small amount of boron is generally desired for fine grain size of the weld metal. The ratio of titanium to boron in the weld metal formed by these prior flux systems was normally at least about 10:1.
The resulting weld metal formed by prior flux systems that included titanium and boron typically required the weld metal to be reheated so as to improve the toughness of the weld metal. When applying multiple layers of weld metal, the lower layer of weld bead can be reheated by the application of a molten weld metal on top of the lower layer of weld metal. However, the top layer of the weld metal is not exposed to another molten layer of weld metal, thus is not reheated during a welding process. As such, this top layer of weld metal can have a reduced hardness. Some prior art fluxes reduced the amount of titanium and boron in the flux system so as to avoid the need to reheat the weld metal; however, the level of titanium in such flux system remained high enough to cause slag removal problems from the weld metal.
In view of the current state of the art of welding fluxes, there is a need for a welding flux that can form high hardness weld metal without the need to reheat the weld metal and which the slag formed during the welding process can be easily removed from the weld metal.